Spinal fixation systems may be used to correct and stabilize the position of vertebral segments within a patient's spine. Such correction may be necessary as a result of accidents, degenerative diseases, etc. Typical spinal fixation systems in use today include pedicle screws attached to the posterior of a patient's vertebrae in a vertical column along either one or both sides of the spine. A rod is connected to the heads of each pedicle screw in a column to provide support for the spine. Examples of such prior art devices may be seen in U.S. Pat. No. 5,741,255 entitled “Spinal Column Retaining Apparatus” to Krag et al. and U.S. Pat. No. 6,187,005 entitled “Variable Angle Spinal Fixation System” to Brace et al.
Unfortunately, when the above prior art systems are inserted in a patient, the pedicle screws are typically positioned such that the head of each pedicle screw angles outward away from the center of the spine (i.e., in a lateral orientation). Because of this screw angle and the fact that the support rods are mounted at about the same height as the pedicle screw heads, there is a significant amount of trauma to the back muscles when this system is installed. This, in turn, leads to a significant amount of pain after the surgery as well as a long recovery time.
Another spinal fixation system is disclosed in U.S. Pat. No. 5,628,740 entitled “Articulating Toggle Bolt Bone Screw” to Mullane. This spinal fixation system is designed for anterior attachment to a patient's spine and includes two columns of screws on either side of the spine with a single support rod therebetween attached to the screws by clamps, as may be seen in FIG. 5 of the patent. However, while such anterior spinal fixation systems may not cause as severe trauma to back muscles (since they are installed on the opposing side of the spine from the back muscles), it may not be possible to install such devices at certain positions on the spine.
Another limitation of the above systems is that their support rods are typically formed as a unitary piece. Even though such support rods typically have some degree of flexibility, they may not be able to accommodate spines that require correction in multiple directions.